The above comments on the appropriate sound level are closely related to the need for low background noise. The difference between the available sound level (the appropriate loudness) and the inevitable background noise is called the dynamic area, and it should be as large as possible.
When talking about background noise, the focus is often on external noise sources – for example traffic noise – but background noise is also generated by technical installations such as projectors, computers and ventilation systems etc.
Photo: In refurbishing Brædstrup School, close attention was paid to the acoustics.
Read more about Brædstrup School.
It is important to pay close attention to background noise, because it can completely ruin the experience of good acoustics in a room. Therefore, it is necessary to specify requirements for background noise, and to adapt the actual requirements according to what the room is going to be used for. Usually, we do not consider this much, but in demanding situations, in other words when we have to strain our ears to hear what is being said, then the problem becomes apparent: it may be in the classroom, where it should be possible to hear the teacher, at the theatre, where the actor’s vocal intensity is a given, limiting factor, or at a restaurant, for example, where it is sometimes difficult to hear what the person sitting opposite us is saying. All three are examples of how background noise can interfere with the primary function and mar the experience.
In small rooms there are rarely problems, but as soon as we find ourselves in rooms designed for teaching, open-plan offices etc., it is important to be aware of the background noise. In really demanding venues such as theatres and concert halls, the requirement for low background noise is simply one of the most important acoustic criteria. If this is overlooked, it can be a very expensive problem.
Notice how concert halls and opera houses often have a large foyer which almost completely surrounds the auditorium.
This is not just so that the audience can enjoy a drink in the interval, but to also create a buffer zone which acoustically insulates the auditorium from the outside world.
Based on experience, the following values are recommended for the maximum acceptable background noise level: